1. Field of the Invention
The present invention relates to a radio frequency (RF) transceiver, and more particularly, to a radio frequency (RF) transceiver capable of preventing a self-quieting occurrence in an advanced mobile phone system (AMPS) communication.
2. Description of the Background Art
FIG. 1 is a schematic block diagram showing a currently used super heterodyne RF transceiver.
As shown in FIG. 1, a signal received through an antenna (ANT) passes a duplexer 1 is amplified by a lower noise amplifier (LNA) 2. The amplified signal is converted into a certain intermediated frequency signal (IF) by a down mixer (4) and recovered to a voice signal by a baseband processor 6.
In transmission, the transmission IF signal generated from the baseband processor is converted into a high frequency transmission signal by an up-mixer 8, amplified by a power amplifier module (PAM) 10, and then transmitted through the antenna after passing the duplexer 1.
When the channel 76 is selected as a communication channel in the AMPS, the receiving channel frequency becomes 872.28 MHz such that the received signal is converted into the IF signal of 85.38 MHz by being mixed with an oscillation frequency of 957.66 MHz generated by a local oscillator 11 at the down mixer 4.
The converted IF signal is filtered by the intermediate frequency filter 5 and sent to the baseband processor 6 so as to be processed for recovering the voice signal.
Also, in case of transmission through the channel 76, the transmission IF signal of 130.38 MHz generated from the baseband processor 6 is converted into a high frequency transmission signal of 827.28 MHz by being mixed with the oscillation frequency of 957.66 MHz generated by the local oscillator 11 at the up-mixer 8 so as to be transmitted through the channel 76.
However, in case that the AMPS transceiver communicates through the channel 76, the reception sensitivity becomes frequently degraded due to a self-quieting.
FIG. 2 is an explanatory view for illustrating the self-quieting phenomenon.
As shown in FIG. 2, in the channel 76, the difference between 1915.32 MHz of the second harmonics of the local oscillation frequency (957.66 MHz) and 1043.04 MHz of the eighth harmonics of the transmission intermediate frequency 130.38 MHz is 872.28 MHz identical to the reception frequency of channel 76.
Accordingly, in case that the AMPS transceiver communicates through the channel 76, the AMPS transceiver generates unexpected frequency component jammer) identical to the receiving high frequency, resulting in degradation of receive sensitivity.